Oil filled cables



Dec. 19, 1961 P. e. PRIAROGGIA EI'AL 3,013,912

OIL FILLED CABLES 5 Sheets-Sheet 1 Filed June 26, 1957 Dec. 19, 1961 P. G. PRIAROGGIA EI'AL 3,01

OIL FILLED CABLES 3 Sheets-Sheet 2 Filed June 26, 1957 Dec. 19, 1961 P. G. PRIAROGGIA ETAL 3,013,912

OIL FILLED CABLES 3 Sheets-Sheet 3 Filed June 26, 1957 United States Patent Ofiice 3,013,912 Patented Dec. 19, 1961 Italy Filed June 26, 1957, Set. No. 668,193 Claims priority, application Italy July 14, 1956 Claims. (Cl. 29-155.5)

The present invention relates to a process for the drying, impregnating and sheathing cables of the oil-filled type, and to devices therefor.

A process is well known according to which the cable core, after a thorough drying under vacuum at l00-ll0 C. passes direct to a sheathing extrusion press. The sheathed cable thus obtained is then placed in a tank heated to a temperature of about 100 (1., wherein it is first submitted to high vacuum to expel any air which may be trapped in the insulation, and is lastly impregnated with fluid oil. With this process, however, there is the disadvantage that very long lengths of cable cannot be treated satisfactorily. It is in fact difiicult to eliminate, by application of vacuum at the two ends, air trapped in the insulating layers of a tubular body of considerable length which is already covered with an impermeable sheath. In this case the action of vacuum is effective only on the end portions of the cable and is ineffective to remove gases and vapors occluded in an intermediate portion if the cable is very long. T o avoid this inconvenience the cable core is, according to another known procedure, dried in a tank under high vacuum and then oil-impregnated in the same tank before being sheathed. In this way, as there is no impermeable sheath, vacuum is effective on the core of the cable also in a radial direction and the air can be evacuated completely even from cables of a substantial length. This second procedure is practiced in tanks comprising a bobbin or pan, on which the cable can be wound in horizontal turns.

For the sake of simplicity these devices are in the present description called horizontal type tanks, to distinguish them from the tank forming the object of the present invention, which is called vertical type tank.

Horizontal tanks known are of two types, i.e.

(a) Rotatable on a vertical axis (1)) Fixed, but with the bobbin or pan rotatable inside the tank.

When a rotatable tank is used it is opened after the impregnation of the cable, and the core to be sheathed is connected to the press by means of a siphon. This system has however the disadvantage that, when the tank is opened, the surface of the insulating oil contained therein is completely exposed to the air.

Moreover a common disadvantage of horizontal tanks of both the rotatable and fixed type resides in that the movement of the bobbin or of the tank must be controlled by an independent means, irrespective of the pull exerted on the cable core from the press, to prevent slippage and uneven winding of the turns of the core,

This is a considerable handicap because it means that an electric motor must be provided to ensure the rotative movement of the bobbin or tank, and also an automatic device is required to control their speed. In addition bobbins or pans, and consequently tanks, of very large diameter must be 'used because otherwise it is difficult to pay off therefrom the cable core disposed in overlying turns.

The object of the present invention is to eliminate the inconveniences of the second system described above.

In the drawings:

FIGURE 1 is a schematical vertical cross-sectional view of a tank for carryingout this invention;

FIGURE 2 is a cross-sectional view on line I'III of FIGURE 1, moreover showing connections of the tank with an oil reservoir and vacuum pump;

FIGURE 3 is a longitudinal sectional view of an end portion of a single-pole cable equipped with a fitting (or head element) employed for performing our method of sheathing;

FIGURE 4 is a fragmentary view showing a manner of hermetically sealing the oil duct in a cable shown on FIG. 3;

FIGURE 5 is a fragmentary view similar to that of FIG. 4, showing a manner of connecting the oil duct in the cable to a source of pressurized oil;

FIGURE 6 is a view similar to that of FIG. 3 relating to a three-pole cable;

FIGURE 7 is a cross-sectional view on line VII-VII of FIG. 6;

FIGURES 8 and 9 are similar to FIGURES 4 and 5 respectively, and show the manner of sealing the oil duct and of connecting the said duct to a source of pressurized oil, respectively, in connection with a cable shown on FIG. 6.

The tank shown in FIGS. 1 and 2 comprises a metallic casing 1, preferably of stainless steel to thereby avoid the possibility of contamination of the insulating oil, which is fixed and has a semi-cylindrical bottom, the casing being surrounded by a heating jacket or heating coils 2. The upper part of the tank is provided with a cover 3 which has a vacuum tight flange and a heating jacket 5, and slopes to one side for the reasons explained below.

(in the opposite side of the tank there is a wide funnel 6, inclined upwardly and provided with a removable vacuum-tight flanged head 7, having a bushing therein which terminates by a socket 8 for supplying electric current to the forward end of the conductor or conductors in the cable core through a hawser 29, which we call here forward hawser.

The funnel 6 extends from the body of the tank and is an integral part of it, thus differing from other known devices where the funnel is an incorporate part of the cover.

The opposite lateral walls of the tankare inwardly provided with pairs of vertical rails 9, forming seats 10 therebetween. The rails thus provide a pair of guides for the op osite hub ends of a bobbin 11 when the latter is slid downwardly into the tank and being rotatably supported therein by the seats 10.

A tubular fitting 13 on the bottom of the tank is provided with a valve 13a, and connects up with an oil reservoir, 1312, while tubular fitting 12 at the top of the tank connects up with a vacuum pump 12b, and is also provided with a valve 12a. The oil reservoir is placed at a level higher than the tank 1.

A plug 14, electrically insulated with respect to the tank, is slidable through a lateral wall of the tank into and out of electrically conductive engagement with a socks 15 on an adjacent flange of the bobbin, which is electrically connected to the inward end of the conductor or conductors in the cable core by means of a hawser 2?, here called tail hawser."

The ends of the cable core to be impregnated and sheathed, are each fitted with a metallic head element for electrically connecting the conductor or conductors in the cable core to the forward and tail hawsers. The head elements are axially bored to allow communication between the inside of the cable core and the outside. Each metallic head element comprises a metallic cap, having an outside diameter substantially equal to that of the cable core. The cap is fitted on the respective ends of the cable core.

FIG. 3 shows a head element applied on an end of the core 17 of a single-phase oil-filled cable.

The end of a conductor strand 18 is bared'by removing the paper insulation 19 for a desired length L1. A tubular plug 20 having a suitable step 21, which serves to lock the end of the steel helix 22 inside the oil duct, is thereupon fitted into the duct itself.

A thin walled metal cap 26, of suitable length and having an outside diameter equal to that of the cable core, is fitted on to each end of the cable core after a few outer layers of insulating paper have been removed through a length L2 proportioned to the length of the cap. The cap has an axially bored extension 23 provided with a cylindrical thread 24. The extension is formed with a cylindrical plug 23:: having a threaded portion 25 and is secured to the conductor strand preferably by pressing it in the region Ll on a hydraulic press.

Each end of the cable core is thus ready to be connected to the hawsers 29 and 29' respectively by means of a suitable connection consisting of a metallic socket 27 soldered to the end of the hawser, either forward 29 or tail 29'.

The socket 27 is prolonged into a springy segmental collet 28 into which the plug 23a of the extension is fitted. The mechanical connection, and the necessary contact for the satisfactory passage of the heating current for the cable conductor between the extension 23 and collet 28 is obtained by screwing on the threaded part 24 a threaded collar or nut 30 which presses the collet segments against the plug 23a on the extension 23.

The axial channel 23b in the extension 23 is aligned with 2011 in the plug 20 and ensures rapid evacuation of the air from the cable core and inflow of impregnating oil into the core.

The end of the oil duct can be closed by screwing a stopper 31, shown in FIG. 4, on the threaded portion 25 by means of a threaded cap 31a.

In the case of a multi-core cable, for instance threecore, the head elements used for the preparation of the ends of the stranded core 32 is similar to that already described and is illustrated in FIG. 6.

The ends of the conductive strands 34, 35 and 36 are bared of insulation for a length L3 and the ends of conductors 35 and 36 are slightly shortened and connected together by means of a metallic connector 37 soldered to them; the end of conductor 34 is fitted into a metallic ferrule 38 and soldered to it. At the other end of the cable core 32 the ends of two other conductors, for example 34 and 35, are connected together also with a corresponding metallic connector 37', while a ferrule 381 is soldered to the end of conductor 36. In this way the electric current could pass through the three conductive strands in series and heat them.

The ferrules 38 and 38' each have four longitudinal grooves 40 on its outside surface. The grooves form channels for the passage of the impregnating oil which flows into the cable core 32 through channels formed by conventional metallic helices 39 provided in the insulation of the conductors.

A thin walled metallic cap 43, having an outside diameter substantially equal to that of the cable core 32, is fitted for a convenient length on to each end of the cable core 32, after some tapes wound over the insulated conductors have been removed. The other end of the cap 43 comprises an axially bored metallic extension 41, enclosing the ferrule 38, which is provided with a cylindrical thread 42. The extension 41 is integral with a cylindrical plug 41a having a threaded portion 48 and is fixed to the ferrule 38 preferably by pressing on a hydraulic press.

The ends of the cable core 32 are thus ready to be connected respectively to hawsers such as 29 and 29' (FIGS. 1 and 2) by means of a connection similar to the one described with reference to FIG. 3, consisting of a socket 44 soldered on the end of the respective hawser,

4 the socket being integral with a springy segmental collet 45 into which the plug 41a is fitted. A threaded collar or nut 46, screwed on the thread 42, presses the collet segments 45 against the plug 41a.

Extension 41 has also in its interior spacers 47 which ensure communication between the channels 40 on the ferrule 33 and the axial channel 415 in the extension 41, thus permitting a rapid evacuation of air from the cable core and entrance of impregnating oil into the latter. The opening of the channel 41b can be closed by screwing a stopper 49 on the threaded portion 48 by means of a threaded cap 49a, as shown in FIG. 8.

The hawsers 29 and 29' connected to the ends of the cable core are insulated metallic strands which serve, in addition to pulling the cable core, also to conduct electric current to the conductor or conductors in the core to heat them during drying of the cable under vacuum.

The forward end of the cable core is connected to hawser 29, which should be of sufficient length to allow both the rotation of the bobin 11, bringing the socket 15 into alignment and engagement with the plug 14 (FIG. 2), and to keep the forward end of the cable core at a suitable distance from the surface of the oil near the flanged head 7 of the tank (FIG. 1) when this head is opened at the end of the impregnating operation, thus exposing the surface of the oil to the outside air.

The inward end of the cable core is connected to the tail hawser 29 which should be long enough to allow the sheathing of the whole length of the cable core without the necessity of disconnecting the tail hawser 29' from socket 15.

The process of drying under vacuum, impregnating with degasified insulating oil, and subsequent sheathing of single-core and multicore oil-filled type cables comprises the following successive operations:

(a) The ends of the cable core are sealed in the manner described above and are connected to hawsers 29 and 29';

(b) The free end of tail hawser 29 is connected to socket 15 (FIG. 2) and then the hawser 29' as well as the cable core to be sheathed and the forward hawser 29 are wound on the bobbin 11 in cylindrical layers coaxial with the bobbin;

(0) The bobbin 11 is placed and supported inside the vertical tank so that it can rotate freely around its own horizontal axis without the necessity of being motor driven. The free end of forward hawser 29 is then connected to the socket 8 (FIG. 1) and the plug 14 is inserted in the socket 15;

(a') Cover 3 and head 7 are closed vacuum tight on the tank which is heated by means of the surrounding jackets 2 and 5; the conductor or conductors in the cable core are also heated during the initial stages of drying at least by means of electric current and vacuum generated in the tank by pumping off the air through the valve 12:: by means of pump 12b (FIG. 2);

(2) After the drying has been completed the tank is no longer heated and the current heating the conductor or conductors is also turned off. The impregnating oil, previously degasified, is then introduced under vacuum into the tank by opening the valve 13a and, when the tank has been filled, the pump 12b is cut off by closing the valve 12a;

(1) When the cable core has been completely impregnated, the valve 13a is almost completely closed and the flanged head 7 is removed. In this manner any oil which has become gassed owing to contact with the outside air can overflow from the top of funnel 6. In addition, as the plug 14 keeps the bobbin 11 blocked in a determined angular position, it is necessary to disconnect it from socket 15 before sheathing so that the bobbin can rotate freely on its axis;

(g) The sheathing is now started by replacing the forward hawser 29 by a steel cable or rope which serves as a tow line to pull the forward end of the cable core through an extension press. For this purpose a piece of approximately 1 to 2 metres of sheathing tube is extruded from the press, which is then stopped, whereupon the -tow line is passed through the press and through the above piece of tube, after the end of funnel 6 has been connected to the press by means of an extensible flexible pipe provided with fluid tight terminal flanges. The forward end of the cable core can now be fitted into the press, following one of the two methods described hereunder.

The first method is the most simple, but less accurate. It consists in bending the extruded piece of tube upwards, and then fully opening the oil valve 13a so that oil overflows out of the end of the extruded piece of tube. The press is thenstarted up and the tow line is pulled so that the cable core is paid off from bobbin 11 until its forward end reaches the entrance to the press.

According to a second method the free end of the extruded tube is sealedfluid tight around the tow line and vacuum is applied in the space between this connection and the free surface of the oil in the funnel 6 by pumping out the air through a pipe branched either from the extensible connecting pipe or from the extruded tube. The oil valve 13a is completely open at this stage so that the above space and the press are filled under vacuum with oil under pressure. Vacuum is then stopped and the press started up. By pulling the tow line the press causes the hawser 29 to advance until the forward end of the cable core is brought to the entrance to the press.

As the forward end enters the extrusion passage in the press the extruded sheath adheres closely to the outer surface of the metallic cap '26 (FIG. 3) or 43 (FIG. 6) on the forward end of the cable core ends and seals it automatically. The cable core is now sheathed still under oil pressure to avoid the danger of air trapping into it whilst it is being paid otf from the bobbin and sheathed.

(11) As soon as the forward end of the cable comes out of the press the sheath G (FIGS. 3 and 6) is cut in the region immediately in preceding the cap 26 (or 43) of the forward metallic head element in the direction of paying out of the cable. When the first piece of sheath has been removed, while keeping the cable under oil pressure the metal ring 30 (or 46) is unscrewed'to disconnect the head hawser from the cable, and the forward end of the cable is connected by means of a flexible tube, 16 in FIG.

5 or 50 in FIG. 9, screwed on thread 25 (FIG. 3) or 48 (FIG. 6) to an oil pressure tank generally installed in the interior of the take-up bobbin for the cable.

By virtue of the length of the tail hawser 29, the entire length of cable core can be sheathed, without disconnecting this hawser from socket 15 (FIG. 1), whilst the metallic cap on the inward end of the cable core is sealed automatically as a result of pressure on the sheath.

At this point the valve for the inflow of oil into the tank is closed, and the sheath G is cut just behind the tail end cap. The threaded collar (such as 30) is then unscrewed to disconnect the ail hawser 29', and a plug 31 (FIG. 4) or 49 (FIG. 8) is screwed on threaded portion 25 or 48 to hermetically seal the inward end of the cable.

No particular care need be exercized to ensure that no air be trapped into the cable through the inward end of the cable because the latter is under oil pressure delivered thereto through tube 16 (FIG. 5) or 50 (FIG. 3) as has been explained heretofore. Multicore cables can also be wound on the take-up bobbin without the necessity of opening the heads to remove the connectors 37 and 37' (FIG. 6) connecting the cable conductors in series. They will be removed later when the ends are opened for acceptance tests or when the cable is put into service.

With the procedure described above it is unnecessary for the bobbin 11 to be driven by electric or other means to ensure rotation because the pull from the press is sufiicient to pay the cable off.

Another feature of the present invention is that the cable ends are sealed by the sheath instantly and automati cally, and any communication between the cable and the exterior is limited to the axial channels 23b and 41b in extensions 23 (FIG. 3) or 41 (FIG. 6) which can be plugged to hermetically sealed in the manner shown in FIGS. 4 and 8.

The fixed vertical type tank described above is designed to be connected, fluid tight, to the sheathing press so that a cable core of the oil-filled type can go direct to the press for sheathing.

It presents some other advantageous characteristics. In fact the inclination of the cover and the semi-cylindrical bottom of the tank make it possible to use a considerably smaller quantity of degasified oil when filling the tank. In addition when the tank is filled and the flanged head 7 is removed the free surface of oil exposed to the air at the top of funnel 6 (FIG. 1) is greatly reduced because the funnel is remarkedly inclined upwardly.

What we claim is:

1. Method of manufacturing cables of the oil-filled type, comprising the steps of manufacturing a dry paper insulated cable core; providing two metallic head elements having a cap portion of an outer diameter at least equalling the diameter of the insulated core and having a hole bored in their bottom; fitting the caps of said metallic head elements on the ends of the insulated core; mechanically joining said metallic head elements to ends of a cable conductor; providing said metallic head elements with forward and tail hawsers; winding said core provided with metallic head elements and hawsers on a tank bobbin; vacuum-drying and impregnating the core in the tank by admitting into the latter degasified oil under pressure; extruding a short length of metal sheathing tube from an extrusion sheathing press; providing a fluid-tight connecting means between the tank and press; causing the forward hawser to extend through said connecting means and extruded length of tube beyond the latter; filling with impregnating oil the connecting means and tube length; drawing the impregnated core by the forward hawser through the connecting means to the press; sheathing the forward core end beyond forward metallic head element, the sheath inner diameter being such that the sheath tightly clamps the cap portion of the metallic head element; cutting and removing the first piece of the sheath in a point preceding the forward metallic head element in the direction of paying out of the cable; connecting the metallic head element hole with a pressure oil reservoir; fully sheathing the impregnated core; cutting and removing the sheath in a point following the tail metallic head element and sealing the hole in said metallic head element.

2. Method as claimed in claim 1, wherein in order to fill with impregnating oil the extruded tube length and connecting means, oil supply to the tank is cut oif, the free opening of said tube length is closed by sealing around a tow line connected to the head hawser, the inside of said connecting means and of the extruded tube length is evacuated and the tank is connected to a pressure oil supply.

3. Method as claimed in claim 1, in which in order to fill with impregnating oil the extruded tube length and connecting means, the extruded tube length is bent upwardly and the tank is connected to its associated oil supply to cause the oil in the tank to rise through said connecting means into said tube length.

4. Method as claimed in claim 1, wherein each metallic head element at least equals in outer diameter the insulated core and prior to fitting each metallic head element on its associated core end region, a layer of insulation is removed from said regions in order to make the diameter thereof just slightly in excess of inner diameter of the metallic head element caps.

5. In the method of impregnating and sheathing a cable core of the character comprising a conductor and a paper insulation enclosing the conductor providing an oil filling channel throughout the core, the steps of fitting on each end section of the core an axially bored metal cap in a fluid-tight relation with a circumferential end surface of the insulation and in a fluid communication between the channel and bore in the cap; then vacuum drying the core; submerging the core in an impregnating oil; pulling one end of the core through an annular sheath-extrusion nozzle while maintaining the core length upstream of the nozzle still submerged in oil and while extruding a sheathing material first onto the cap fitted on the said one end of the core and then onto the core and finally onto the other cap thereby sealing the caps and core under the sheath material; and delivering oil pressure into the channel through the bore in the cap fitted on the said 8 one end of the core while extruding the sheathing material onto the core and the said other cap.

References Cited in the file of this patent UNITED STATES PATENTS 1,957,995 Emanueli H May 8, 1934 1,978,050 Johnson Oct. 23, 1934 2,024,144 Chase Dec. 17, 1935 2,235,824 Cary Mar. 25, 1941 2,781,285 White Feb. 12, 1957 2,831,656 Grieve Apr. 22, 1958 FOREIGN PATENTS 11,048 Great Britain June 29, 1891 

1. METHOD OF MANUFACTURING CABLES OF THE OIL-FILLED TYPE, COMPRISING THE STEPS OF MANUFACTURING A DRY PAPER INSULATED CABLE CORE; PROVIDING TWO METALLIC HEAD ELEMENTS HAVING A CAP PORTION OF AN OUTER DIAMETER AT LEAST EQUALLING THE DIAMETER OF THE INSULATED CORE AND HAVING A HOLE BORED IN THEIR BOTTOM; FITTING THE CAPS OF SAID METALLIC HEAD ELEMENTS ON THE ENDS OF THE INSULATED CORE; MECHANICALLY JOINING SAID METALLIC HEAD ELEMENTS TO ENDS OF A CABLE CONDUCTOR; PROVIDING SAID METALLIC HEAD ELEMENTS WITH FORWARD AND TAIL HAWSERS; WINDING SAID CORE PROVIDED WITH METALLIC HEAD ELEMENTS AND HAWSERS ON A TANK BOBBIN; VACUUM-DRYING AND IMPREGNATING THE CORE IN THE TANK BY ADMITTING INTO THE LATTER DEGASIFIED OIL UNDER PRESSURE; EXTRUDING A SHORT LENGTH OF METAL SHEATHING TUBE FROM AN EXTRUSION SHEATHING PRESS; PROVIDING A FLUID-TIGHT CONNECTING MEANS BETWEEN THE TANK AND PRESS; CAUSING THE FORWARD HAWSER TO EXTEND THROUGH SAID CONNECTING MEANS AND EXTRUDED LENGTH OF TUBE BEYOND THE LATTER; FILLING WITH IMPREGNATING OIL THE CONNECTING MEANS AND TUBE LENGTH; DRAWING THE IMPREGNATED CORE BY THE FORWARD HAWSER THROUGH 